A report by the Senate Intelligence Committee concludes that the CIA misled the government and the public about aspects of its brutal interrogation program for years — concealing details about the severity of its methods, overstating the significance of plots and prisoners, and taking credit for critical pieces of intelligence that detainees had in fact surrendered before they were subjected to harsh techniques.

The report, built around detailed chronologies of dozens of CIA detainees, documents a long-standing pattern of unsubstantiated claims as agency officials sought permission to use — and later tried to defend — excruciating interrogation methods that yielded little, if any, significant intelligence, according to U.S. officials who have reviewed the document.

“The CIA described [its program] repeatedly both to the Department of Justice and eventually to Congress as getting unique, otherwise unobtainable intelligence that helped disrupt terrorist plots and save thousands of lives,” said one U.S. official briefed on the report. “Was that actually true? The answer is no.”

Current and former U.S. officials who described the report spoke on the condition of anonymity because of the sensitivity of the issue and because the document remains classified. The 6,300-page report includes what officials described as damning new disclosures about a sprawling network of secret detention facilities, or “black sites,” that was dismantled by President Obama in 2009.

Classified files reviewed by committee investigators reveal internal divisions over the interrogation program, officials said, including one case in which CIA employees left the agency’s secret prison in Thailand after becoming disturbed by the brutal measures being employed there. The report also cites cases in which officials at CIA headquarters demanded the continued use of harsh interrogation techniques even after analysts were convinced that prisoners had no more information to give.

The report describes previously undisclosed cases of abuse, including the alleged repeated dunking of a terrorism suspect in tanks of ice water at a detention site in Afghanistan — a method that bore similarities to waterboarding but never appeared on any Justice Department-
approved list of techniques.

U.S. officials said the committee refrained from assigning motives to CIA officials whose actions or statements were scrutinized. The report also does not recommend new administrative punishment or further criminal inquiry into a program that the Justice Department has investigated repeatedly. Still, the document is almost certain to reignite an unresolved public debate over a period that many regard as the most controversial in CIA history.

A spokesman for the CIA said the agency had not yet seen a final version of the report and was, therefore, unable to comment.

Current and former agency officials, however, have privately described the study as marred by factual errors and misguided conclusions. Last month, in an indication of the level of tension between the CIA and the committee, each side accused the other of possible criminal violations in accessing each other’s computer systems during the course of the probe.

The Senate Intelligence Committee is expected to vote Thursday to send an executive summary of the report to Obama for declassification. U.S. officials said it could be months before that section, which contains roughly 20 conclusions and spans about 400 pages, is released to the public.

The report’s release also could resurrect a long-standing feud between the CIA and the FBI, where many officials were dismayed by the agency’s use of methods that Obama and others later labeled torture.

CIA veterans have expressed concern that the report reflects FBI biases. One of its principal authors is a former FBI analyst, and the panel relied in part on bureau documents as well as notes from former FBI agent Ali Soufan. Soufan was the first to interrogate Zayn al-Abidin Muhammed Hussein, the suspected al-Qaeda operative better known as Abu Zubaida, after his capture in Pakistan in 2002 and has condemned the CIA for water­boarding a prisoner he considered cooperative.

The Senate report is by far the most comprehensive account to date of a highly classified program that was established within months of the Sept. 11, 2001, attacks, a time of widespread concern that an additional wave of terrorist plots had already been set in motion.

‘Damaging’ misstatements

Several officials who have read the document said some of its most troubling sections deal not with detainee abuse but with discrepancies between the statements of senior CIA officials in Washington and the details revealed in the written communications of lower-level employees directly involved.

Officials said millions of records make clear that the CIA’s ability to obtain the most valuable intelligence against al-Qaeda — including tips that led to the killing of Osama bin Laden in 2011 — had little, if anything, to do with “enhanced interrogation techniques.”